Utility knives that incorporate retractable, replaceable razor blades are well known in the art. Utility knives are very versatile, enjoying popularity with the professional construction worker, the domestic handyman, and the amateur hobbyist alike. Utility knives generally include a retractable razor blade mounted within a protective handle or housing. The blade is fastened to a support structure such as a blade carrier or blade pusher, which extends through the surface of the housing. In operation, the blade is extended by sliding the blade holder forward. One deficiency of the prior art designs is that the blade may be inadvertently deployed, becoming a safety hazard. For example, if the blade holder catches on a pocket or a tool belt or is jostled by another tool in a toolbox, the blade may be deployed unbeknownst to the user. An unwary user reaching for a utility knife with the blade deployed can easily receive a severe cut.
There have been attempts in the prior art to address this problem. For example, U.S. Pat. No. 5,890,294 to Keklak et al. discloses a locking safety utility knife having an operating lever that deploys a blade when squeezed and a ratchet-like locking mechanism releasable by manipulation (depression) of a cam located at the end of the knife. However, the Keklak et al. device still exhibits the problem of accidental disengagement of the safety if the cam is accidentally depressed, allowing the knife to accidentally open and deploy the blade. Moreover, the cam is located on the end of the knife, increasing the likelihood of accidental depression.
Other known utility knives known in the art have sliding blades that are locked by blade holders that must be depressed as they are slid forward to engage the blade. Again, since the unlocking force and the deploying force may be resolved into a single angular force acting upon the blade holder, accidental release of the blade can readily occur if the blade holder catches on the user's clothing or on another tool.
There is therefore a need in the art for a safety mechanism for a utility knife that cannot be accidentally disengaged through the simple depression of a switch or cam. The present invention satisfies this need.